Like Cyrus, who rose to fame as the star of Disney's "Hannah Montana" franchise, Bynes, 27, is a former child star. The actress, who once had her own show on Nickelodeon and later starred in movies such as "Hairspray," is currently receiving psychiatric help in a private facility following a personal breakdown, during which she also posted a slew of tweets bashing celebrities, and after being detained on a 5150 hold.

O'Connor, 46, has not reacted to Cyrus' response, which was retweeted more than 4,100 times.

"@MileyCyrus queen," one fan responded.

Also, another photo was posted on Cyrus' Twitter page in response to O'Connor -- a screenshot of the singer's controversial 1992 performance on "Saturday Night Live," which shows her ripping up a photo of the Pope. Cyrus is set to host and perform on the NBC show this weekend (watch a promo VIDEO).

Cyrus has made headlines over a racy MTV VMAs performance and her semi-nude "Wrecking Ball" music video. In her letter, which was posted on her website, O'Connor had told Cyrus that the music business will "prostitute" her and make it seem like it is her idea. O'Connor also said Cyrus was talented and that female singers are role models who should be careful about the messages they send to other women.